The present invention relates to an ink-jet printer, in particular to its capping mechanism.
An ink-jet printer has a printing head provided with a plurality of pressure chambers, to which ink is supplied from a cartridge. Pressure is created in the chambers by piezoelectric means, for example, or more commonly by heating the ink so that it partially vaporizes. The pressure ejects a drop of ink through a fine nozzle, thereby printing a pixel on a sheet of paper. To print a page, the print head moves back and forth on a movable carriage mounted on a shaft, ejecting drops on demand according to print data.
The diameter of the nozzles is typically no more than twenty to sixty micrometers (20-60 .mu.m), so if the ink in the chambers were allowed to dry out during non-printing periods, the nozzles could easily become clogged with viscous or hardened ink. Accumulation of dirt (particles of dried ink, paper, etc.) around the nozzles can also cause clogging, or cause ink drops to be ejected in the wrong direction. These problems show up as printing defects such as missing or misplaced pixels.
To prevent these problems, an ink-jet printer is conventionally designed so that during non-printing periods, the print head moves to a parking station where it is covered by a cap. The print head normally remains capped while power is switched off. Many conventional printers are also designed, however, so that the carriage can be moved manually while power is off. If the carriage is thus moved, to facilitate the replacement of an ink cartridge for example, the operator may forget to move the carriage back to its parking station, so that the print head is left uncapped. Printing defects then appear when the printer is next used.
One way to keep the print head from being left inadvertently uncapped would to be provide a locking mechanism that holds the carriage at the parking station while power is off. This is not a desirable provision, however, because a person not knowing of the existence of the locking mechanism might attempt to move the carriage by force, resulting in damage to the printer.